The present invention relates to slurry compositions. The slurry compositions are useful for polishing and especially for planarizing surfaces in the microelectronics industry.
More particularly the present invention relates to increasing selective polishing rates by employing slurry compositions containing polyelectrolytes. Anionic polyelectrolytes increase the selectivity rate of silicon dioxide to silicon nitride. Cationic polyelectrolytes increase the selectivity polishing rate of metals to silicon dioxide, silicon nitride and/or silicon oxynitride.
In the fabrication of microelectronics components, a number of steps involved are polishing, especially surfaces for chemical-mechanical polishing for the purpose of recovering a selected material and/or planarizing the structure.
Accordingly, over the years, a number of vastly different types of polishing processes to remove material, sometimes in selective areas, have been developed and are utilized to varying degrees.
In many microelectronics applications a Si3N4 layer is deposited under a SiO2 layer to serve as a polish stop. The role of such polish stop is particularly important in Shallow Trench Isolation (STI) structures. Selectivity is characteristically expressed as the ratio of the oxide polish rate to the nitride polish rate. State of the art polishing slurries such as silica slurry at alkaline pH, or ceria slurry at neutral or alkaline pH have an oxide to nitride selectivity of about 3. Such ratio is not high enough for the nitride to adequately serve as a polish stop.
It could also therefore be desirable to provide a polishing procedure which achieved excellent removal of silicon dioxide along with exhorting an increased polishing selectivity rate as compared to silicon nitride.
Also in other microelectrics structures, a layer of silicon dioxide, silicon nitride and/or silicon oxynitride insulator is located beneath a metal layer such as a copper, tungsten or aluminum layer and a liner such as Ti, TiN, Ta and TaN to act as a polish stop. If the polishing rate selectivity of the metal to the underlying silicon dioxide, silicon nitride and/or silicon oxynitride can be increased, the liner might possibly be eliminated.
It could also therefore be desirable to provide a polishing procedure which achieves excellent removal of a metal along with exhibiting an increased polishing selectivity rate as compared to silicon dioxide, silicon nitride and/or silicon oxynitride.
The present invention provides for increasing the polishing rate ratio of silicon dioxide to silicon nitride by including a polyelectrolyte in the polishing slurry. The present invention also provides for increasing the rate ratio of a metal to silicon dioxide, silicon nitride and/or silicon oxynitride, by including a polyelectrolyte in the polishing slurry.
More particularly, an aspect of the present invention relates to a polish composition comprising abrasive particles and about 0.05 to about 5% by weight of an anionic polyelectrolyte or a cationic polyelectrolyte.
Another aspect of the present invention relates to a method for polishing a silicon dioxide surface which is in contact with silicon nitride by providing on the silicon dioxide a composition comprising abrasive particles and an anionic polyelectrolyte in an amount sufficient to increase the polishing rate ratio of the silicon dioxide to silicon nitride.
Another aspect of the present invention relates to a method for polishing a metal surface which is in contact with silicon dioxide, silicon nitride and/or silicon oxynitride by providing on the metal surface a slurry comprising abrasive particles and a cationic polyelectrolyte in an amount sufficient to increase the polishing rate ratio of the metal to the silicon dioxide, silicon nitride and/or silicon oxynitride.
According to the present invention a polishing slurry that contains abrasive particles and polyelectrolytes is provided. The polyelectrolytes increase the polishing rate selectivity of certain surfaces depending upon the type of polyelectrolytes employed. In particular, anionic polyelectrolytes increase the polishing rate selectivity of silicon dioxide as compared to silicon nitride.
On the other hand, cationic polyelectrolytes increase the polishing rate selectivity of metals as compared to silicon dioxide, silicon nitride and/or silicon oxynitride.
According to the present invention, in order to achieve increased selectivity, the quantity of polyelectrolytes in the abrasive composition is in excess of the amount which adsorbs on the surface of the abrasive particles and therefore is present to some extent in the composition as free or unabsorbed polyelectrolyte. The polyelectrolyte is typically added to the abrasive composition in an amount of at least about 0.05% by weight and more typically about 0.05 to about 5% of weight and preferably about 0.3 to about 1% by weight.
While a fraction of the polyelectrolyte may adsorb on the surface of the abrasive particles, the rest of the polyelectrolyte is in the supernatant part of the slurry. It is this portion of the polyelectrolyte which controls the polish rate selectivity.
Anionic polyelectrolytes contemplated for use according to the present invention can contain acidic groups such as carboxyl groups, for example in poly (acrylic acid), poly (methacrylic acid), poly (methyl methacrylic acid), poly (maleic acid), saturated and unsaturated poly (carboxylic acids) and copolymers thereof. Also, phosphoric acid and/or sulfonic acids groups can be incorporated into a polymer and may act as acidic functional group such as poly (vinylsulfonic acid).
Cationic polyelectrolytes contemplated for use according to the present invention can contain basic groups including nitrogen-containing groups, such as polymers with amino, amide, imide, vinyl pyridine, piperidine and piperazine derivatives. Examples of specific cationic polyelectrolytes are poly (vinylamine), poly (ethylenimine) and poly (4-vinylpryridine).
Typically the polyelectrolytes employed according to the present invention have relatively low molecular weights of less than about 100,000 and more typically about 300 to about 20,000 weight average molecular weight.
Examples of suitable abrasive particles include alumina, ceria, silica, and zirconia. The abrasives typically have a particle size of about 30 to about 1000 nanometers and preferably about 75 to about 300 nanometers.
The amount of abrasive particles is typically about 0.1 to about 20 percent by weight and more typically about 0.3 to about 2 percent of weight.
The slurry can include other ingredients in addition to the abrasive and polyelectrolyte such as dispersing agents and oxidizing agents, if desired.
The slurry is preferably an aqueous slurry, though non-water-based slurries or a mixture of water based and non-water-based slurries are included in the present invention.
The parameters of the polishing or planarizing can be determined by those skilled in the art, once aware of this disclosure, without exercising undue experimentation. For instance, the speed of rotation of the polishing pads and also of the wafer is about 10 to about 150 rpm and pressure about 2 to 10 psi. A wafer may be in the range of 100 to 300 mm in diameter.